In comparison with the polycarbonates customarily prepared with phenol, 2,6-dimethylphenol and p-tert.butylphenol, as a chain regulator, the polycarbonates according to the invention exhibit a substantially increased resistance to hydrolysis and an improved critical width, the mechanical and thermal properties being otherwise comparable.
Compared with the polycarbonates of Japanese Laid-Open Specification No. 34,992/76, in which, inter alia, p-nonphenol is employed as a chain stopper for the preparation of polycarbonates (see Example 5 of Japanese Laid-Open Specification No. 34,992/76), the polycarbonates according to the invention exhibit no lowering of the heat distortion point, which could not be foreseen. (See the heat distortion point values in Japanese Laid-Open Specification 34,992/76: for Comparison Example 1, with p-tert.-butylphenol as the chain stopper =135.degree. C., and for Example 5, with p-nonylphenol as the chain stopper =128.degree. C.; and see also the Vicat B temperature for Comparison Examples 3 and 5 of the present patent application).
The polycarbonates of Japanese Laid-Open Specification 34,992/76 moreover exhibit no improvements in the resistance to hydrolysis and in the critical width compared with conventional polycarbonates prepared with phenol as a chain stopper. (See Comparison Examples 4 and 5 of the present patent application).